1. Field of the Invention
The invention relates to rare-earth doped phosphate laser glasses and methods of generating pulses of laser light in a laser system using such laser glasses.
2. Background of the Invention
It was first recognized that neodymium (Nd) doped laser glass could serve as a lasering material or gain medium over forty years ago (E. Snitzer, “Optical Maser Action in Barium Crown Glass,” Physical Review Letters 7, 444 (1961)). The Nd-doped glass is energized with a pump source, such as a flashlamp of other laser components such as laser diodes, so that the material exhibits gain near the lasing wavelength. For example, in the case of Nd-doped barium crown glass the lasing wavelength is 1054 nm. In this way, it is possible to amplify or generate laser light within the gain medium, i.e., the laser glass.
Following the recognition that Nd-doped glass was a useful gain medium, there were numerous developments in the area of laser glass in which particular formulations and compositions were developed with properties specifically tailored to match individual applications. Phosphate glasses were one area that received particular attention from the scientific community. The first Nd-doped phosphate laser glass patents focused solely on the composition of the glass material itself (DePaolis et al., U.S. Pat. No. 3,250,721). Later, Deutschbein et al. disclosed Nd-doped phosphate laser glass compositions having low thermal expansion and negative temperature coefficient of refractive index (dn/dT) making possible the design of solid-state laser systems with optical pathlength nearly independent of changes in device temperature (see U.S. Pat. No. 4,022,707).
Alexeev et al., in U.S. Pat. No. 3,979,322, combined the use of negative dn/dT values along with higher values for stimulated emission of laser light (σemm), and claimed more limited phosphate glass compositions specific for Nd-lasers. Later patents disclosed Nd-doped laser glass compositions that provide for: reduced glass transition temperature, the temperature at which glass properties such as refractive index are subsequently influenced by exposure to high temperature (U.S. Pat. No. 4,996,172 by Beall et al.); improved thermal shock resistance (e.g., high fracture toughness) in combination with good laser properties (U.S. Pat. No. 4,929,387 by Hayden et al., U.S. Pat. No. 5,053,165 by Toratani et al., and U.S. Pat. No. 5,032,315 of Hayden et al.); chemical strengthening techniques (U.S. Pat. No. 5,164,343 by Myers); a desirable athermal behavior (U.S. Pat. No. 4,075,120 and U.S. Pat. Nos. 4,333,848 by Myers et al. and 4,108,673 by Izumitani et al.); sensitized laser glasses (U.S. Pat. No. 4,770,811 by Myers); glasses with reduced concentration quenching behavior (U.S. Pat. No. 4,371,965 by Limpicki et al., U.S. Pat. No. 4,470,922 by Denker et al., and U.S. Pat. No. 4,661,284 by Cook et al.); glasses characterized by low values of emission cross section σemm (U.S. Pat. No. 5,173,456 by Hayden et al.); and glasses with properties enhanced for manufacturing yield in combination with improved performance in high peak energy laser systems (U.S. Pat. No. 5,526,369 by Hayden et al.). In addition, U.S. Pat. No. 4,820,662 by Izumitani et al., discloses phosphate glass compositions that contain SiO2 as a required additive which also contain rare-earths (specifically neodymium) up to 12 mol % on an oxide basis. The aforementioned patents are cases where rare-earth-doped, in particular neodymium-doped, glass compositions were tailored to offer properties favorable for specific laser application examples.